Low-migration copper alloy

ABSTRACT

The present invention relates to a copper alloy, in particular for components which carry media or drinking water, in particular fittings, valves or compression joints and also an advantageous use of the copper alloy and components for lines carrying media or drinking water. It is an object of the present invention to provide a copper alloy which has good corrosion resistance, good castability and mechanical workability and also good mechanical properties and displays good migration values, particularly in respect of the migration of lead and nickel ions into drinking water. The copper alloy provided for this purpose by the present invention comprises from 2% by weight to 4.5% by weight of silicon, from 1 to 15% by weight of zinc and from 0.05% by weight to 2% by weight of manganese. Furthermore, from 0.05 to 0.4% by weight of aluminium and from 0.05 to 2% by weight of tin can optionally be present. As balance, the copper alloy contains copper and unavoidable impurities.

The present invention relates to a copper alloy. In particular. the present invention relates to a low-migration copper alloy for the manufacture of components for gas and sanitary installations, especially for components which are employed in drinking water installations and are in direct contact with the drinking water carried in the components, as a rule pipes, fittings and valves.

Materials for the manufacture of components for gas and water installations are subject to particular demands which are in particular placed on lines carrying drinking water as well as their elements. Here, primarily the corrosion resistance of the components has to be mentioned, for the installed components must not corrode even if they are employed for several years. Moreover, particular demands are placed on the manufacturability and processability, where it must not only be possible to cast the alloys easily and economically but where it moreover is necessary for the cast components to be easily mechanically worked. Here, in particular good machinability has to be paid attention to. Finally, the components made of the copper alloy also have to withstand the mechanical strains required for the field of employment. Thus, in copper-tin-zinc alloys, a tensile strength of more than 180 N/mm² at a 0.2% proof stress of 85 N/mm² is always considered to be necessary. With bronzes (copper-tin alloys) the tensile strength should be 240 N/mm² and the 0.2% proof stress 130 N/mm² and more.

Furthermore, the behavior of the materials with respect to the emission of ions of the alloy components of the materials or of reaction products with water ingredients is of particular interest. Here, very narrow limits with respect to the allowed emission of metal ions from the components into the drinking water have to be observed for protecting the consumer.

Apart from other alloys, today also highly coppery nonferrous heavy metal alloys, such as bronze or red bronze, are employed for the manufacture of the components of gas and water lines carrying media. With respect to good mechanical workability, certain amounts of lead are added to these nonferrous heavy metal alloys. For increasing corrosion resistance and strength, the addition of nickel is to be preferred.

Common representatives of bronze-cast alloys are summarized in DIN EN 1982. By way of example, here the red bronze alloy CuSn5Zn5Pb5 with between 4 to 6% by weight of tin, zinc and lead each, with a content of up to 2.0% by weight of nickel and up to 0.1% by weight of phosphorous as well as additions of up to 0.3% by weight of iron and up to 0.25% by weight of antimony are mentioned. It is true that this material is characterized by good castability as well as good corrosion resistance even with respect to sea water. With respect to the emission of metal ions into the water, however, this material has to be considered as not being satisfactory in view of the limiting values to be expected in future. Here, in particular the high lead emission of CuSn5Zn5Pb5 is criticized.

With the EP-1 045 041, a lead-free copper alloy has already been suggested which is said to have satisfactory machinability and which comprises up to 79% by weight of copper, between 2 and 4% by weight of silicon, and as balance zinc. This alloy is especially taken into consideration for the manufacture of valves, fittings and similar parts for water carrying pipe systems. However, in particular with respect to corrosion resistance, the alloy does not behave as red bronze and can consequently not substitute the same.

GB-1 443 090 discloses a copper alloy improved with respect to dezincification with between 80 and 90% by weight of copper, between 6.3 and 17.5% by weight of zinc, and between 2.8 and 4.75% by weight of silicon as essential alloy components with between 0.03 and 0.05% by weight of arsenic. For improving the corrosion properties, according to the solution of the GB-1 443 090, a heat treatment of the cast parts is suggested. In this heat treatment, the cast parts are annealed at temperatures of between 600° C. and 750° C. over a period of 5 to 10 days and subsequently quenched. This heat treatment is performed with the aim of obtaining the α and ζ-phases to be preferred with respect to corrosion. By quenching, in particular the formation of phases of which the corrosion resistance is low, e.g. the μ- and χ-phases, is to be avoided.

From GB-1 385 411, a copper alloy is known which has up to 10% by weight of aluminum and up to 5% by weight of iron and is employed for the manufacture of components of water installations carrying water. This alloy, however. has an insufficient corrosion behavior and in particular migration of metal ions into the water is too high.

The problem underlying the present invention is to provide a copper alloy improved with respect to the migration behavior which is in particular suited for the manufacture of gas and water lines carrying media and their parts and which has good corrosion resistance with respect to media, good strength and good workability and castability. For the workability, in particular the machining properties of the copper alloy are very important. Moreover, the invention wants to provide corresponding medium-carrying components, in particular fittings or valves, as well as an advantageous use of the copper alloy according to the invention.

With respect to the substance-related aspect of the present invention, the same suggests a copper alloy with the features of claim 1. This copper alloy comprises between 2 and 4.5% by weight of silicon, between 1 and 15% by weight of zinc and between 0.05 and 2% by weight of manganese. Apart from these necessary elements, the copper alloy can contain between 0.05 and 0.5% by weight of aluminum and/or between 0.05 and 2% by weight of tin. As balance, copper and unavoidable impurities are contained in the alloy. These impurities are preferably restricted to a proportion of 0.5% by weight. Particularly preferred, the upper limit for the impurities is 0.25%. This upper limit in particular applies to the cumulative proportion of nickel and lead in the alloy, which proved to be a particularly effective measure for suppressing the migration of lead or nickel, respectively. With respect to this, the alloy is preferably free from lead and/or nickel. An alloy in which the proportion of lead is less than 0.25% is considered as lead-free alloy. An alloy in which the proportion of nickel is less than 0.15% is considered as nickel-free alloy.

The alloy should contain between 0.01 and 0.05% by weight of zirconium. Preferably, the zirconium proportion should be between 0.01% by weight and 0.03% by weight; particularly preferred, the upper limit is determined to be 0.02% by weight. This interval applies for essentially all cast components, except for sand castings. Grain refining usually results only as of 0.01% by weight, above 0.02% by weight, the risk of zirconium formation in the grain boundary zone is increased. Zirconium improves the solidification morphology and reduces the formation of heat cracks, mainly in permanent mold casting. In particular in castings which are made by means of sand casting, a deliberate addition of zirconium, however, can be dispensed with. In these components, the zirconium proportion can be below 0.01% by weight, preferably even below 5 ppm (0.0005%).

The stated preferred upper limit for zirconium of 0.02% should be observed to avoid zirconium formation in the grain boundary zone of the texture which leads to increased tool wear in the machining of the components cast from the alloy for water-carrying lines.

Optionally, phosphorous should also be provided in certain proportions. Phosphorous is preferably present with a proportion of 0.01% by weight to 0.2% by weight. Phosphorous is controlled in stated limits in particular with respect to an improvement of castability (flowability and feeding behavior of the alloy). Further, phosphorous reduces the dezincification of the alloy and improves corrosion resistance. However, it showed that with a phosphorous content of more than 0.2% by weight, the alloy becomes increasingly harder, which results in problems in the machining of cast components.

It showed that with a copper alloy according to the invention, as it is stated in claim 1, the demands to be placed on components for medium-carrying gas or water lines can be met best. The alloy shows good casting behavior. The components made by casting can be easily machined. Tests with test pieces showed that the strength corresponds to the demands to be placed. Moreover, the corrosion resistance of the alloy is high. It showed that by controlling the phosphorous content in the alloy, the reject rate of the castings can be limited. Correspondingly, the degree of impurities for phosphorous is preferably controlled to a range of 0.01 to 0.05% by weight.

The aluminum content of the copper alloy according to the invention is determined with regard to the corrosion resistance of the same. At present, it is assumed that with an aluminum content of between 0.05 and 0.5% by weight, good corrosion resistance can be achieved. Without considerable quality losses, the upper limiting value for the aluminum content can be determined to 0.4% by weight.

It could be confirmed in practical tests that the relevant components for medium-carrying lines can be easily made with the usual casting methods, for example sand casting. permanent mold casting, centrifugal casting or continuous casting. With respect to the quenching conditions from the melt, there are no particular demands. The casting obtained in this manner can be easily machined. For reducing the migration tendency of the casting. the same can preferably be subjected to a heat treatment before machining. In the process, the casting is preferably annealed at between 400° C. and 800° C. for at least half an hour. Preferably, the heat treatment is performed at a temperature interval of between 600° C. and 700° C. The annealing time can be arbitrarily long. With respect to economic margin conditions, it is, however, determined to between 2 and 16 hours. The heat up phase is not included in this annealing time.

Annealing is performed in particular with the aim of adjusting the α-phase in the cast component which permits the combination of various properties to be achieved according to the present idea of the inventors. It should be pointed out, however, that already the major part of the necessary alloy elements copper, zinc and silicon solidifies in the form of an α-solid solution with natural quenching from the melt without separate heat treatment.

An addition of silicon within the given intervals further favors chip breakage during working. With an increased silicon content, however, the tool wear in the machining of the components made from the alloy is also increased. Correspondingly, the upper limit for the silicon content is determined to 4.5% by weight, not least also in view of the mechanical workability of the alloy.

In view of the required corrosion resistance, in the copper alloy according to the invention, the zinc content is limited to 15% by weight. A minimum content of 1% by weight of zinc in contrast guarantees a minimum of machinability.

Manganese is added to the alloy within the limits of 0.05 to 2% by weight to improve the texture. Manganese improves the texture and has a positive influence on the solidification behavior of the copper alloy. However, the manganese content is limited to 2% by weight with regard to the migration tendency of manganese.

With a restriction of the sum of impurities to maximally 0.5% by weight, the content of ingredients which could possibly migrate into the drinking water is also restricted to a minimum selected under economic points of view. With a further restricted upper limiting value for the unavoidable impurities of 0.25% by weight, better security against migration can be achieved, however at the cost of the manufacturing costs.

Preferably, the alloy according to the invention contains between 5 and 15% by weight of zinc. In this restricted interval, a best possible combination of corrosion resistance and machinability can be achieved.

For optimizing the strength with adequate strain properties of the material in combination with good migration values, the silicon content is determined to between 2.8% by weight and 4% by weight.

For further reducing the migration tendency of manganese, its content is preferably determined to 0.2 to 0.6% by weight. For the same reasons, the alloy preferably does not contain any nickel or lead, respectively. The copper content in the alloy should be at least 80 and maximally 96.95% by weight.

According to a second aspect of the present invention, the use of the copper alloy according to the invention is suggested for the manufacture of components for medium-carrying gas and water lines, respectively. These are in particular such components which form drinking water lines, such as in particular fittings and valves as well as parts thereof. Not least due to the good stress-strain properties of the copper alloy according to the invention. preferably a compression joint is to be made from the copper alloy according to the invention. The compression joints can be either formed as separate components or be provided at the fitting or the valve with a substance- or form-fit. The compression joints can be also realized as integral parts in the casting of the valve or the fitting from the copper alloy according to the invention. The casting alloy according to the invention is in particular suited for the manufacture of an element of a compression joint arrangement, as they are known, for example, from EP 0 343 395 or DE 10 2004 031 247.

The invention will be illustrated below with reference to an embodiment in connection with the drawing, wherein:

FIG. 1 shows a diagram with a comparison of the lead migration of an embodiment of the copper alloy according to the invention with respect to a conventional red-bronze alloy;

FIG. 2 shows a diagram with a comparison of the nickel migration of an embodiment of the copper alloy according to the invention with respect to a conventional red-bronze alloy;

FIG. 3 shows a diagram with a comparison of the copper migration of an embodiment of the copper alloy according to the invention with respect to a conventional red-bronze alloy; and

FIG. 4 shows a diagram with a comparison of the zinc migration of an embodiment of the copper alloy according to the invention with respect to a conventional red-bronze alloy.

FIGS. 1 to 4 show the time history of the emission of certain metal ions in a set-up of measuring instruments according to DIN 50931-1 over a time of altogether 26 weeks. Here, the DIN determines the test set-up and the test conditions by means of which the corrosion probability of materials for metallic components of a drinking water installation in case of a corrosion contamination of drinking water can be determined.

In each case, the time history for the use of an embodiment of a copper alloy according to the invention with the following composition is shown:

Si: 3.5% by weight;

Zn: 1.6% by weight;

Mn: 0.5% by weight;

sum of unavoidable impurities: max. 0.5% by weight;

and as balance copper.

The results in the respective representations of FIGS. 1 to 4 are compared with those measured values that can be achieved in a conventional red-bronze alloy with the same test conditions. The red-bronze alloy has the following composition:

Zn: 5.5% by weight;

Sn: 4.5% by weight;

Pb: 3.0% by weight;

Ni: 0.5% by weight;

Balance: copper and unavoidable impurities.

The measuring results with the embodiment of the copper alloy according to the invention are marked with A. The comparison measurement with the red-bronze alloy is marked with B.

Apart from the aforementioned comparison, FIGS. 1 to 3 also contain a limiting value according to the German Drinking Water Regulation (DrinkwR) for the emission of certain ions into water and the parameter value W(15) to be observed in migration tests. This parameter value W(15) has to be observed if an excess of the value of the DrinkwR is to be avoided when the tested component is used. The parameter value W(15) results from the product of the limiting value according to the DrinkwR and the relation of the form factors A and B. The form factor A results according to DIN 50931 -1 from the relation of the surface of the material contacted by water to the surface of the complete test arrangement contacted by water. The form factor B is a scaling factor according to DIN 50930-6 which takes into consideration the type of the components.

FIG. 1 illustrates that the amount of lead emission of the red-bronze alloy falls within the first four test weeks nearly exponentially from a very high value, higher tan 50 μg/l, to a value which settles just above the limiting value of the German DrinkwR of 10 μg/l after 12 to 26 test weeks. It is assumed that this clear excess at the beginning of the tests is due to the fact that lead that has reached the surface of the component to be tested due to the working and manufacture migrates into the drinking water After the first weeks, the surface-near lead has migrated from the sample body and the amount of the emitted lead remains approximately constant.

The embodiment according to invention A, however, emits nearly no lead to the drinking water. An increased value at the beginning of the tests can neither be identified. As the measured values are at the boarder of discrimination of the measuring analysis, the fluctuations of the measured values are attributed to the measuring accuracy of the measuring instruments. Essentially, the measured value for the lead emission remains clearly below the limiting value of the DrinkwR of 10 μg/l in the sample according to the invention.

The same goes for the nickel emission of the compared samples represented in FIG. 2. The comparison sample from the red-bronze alloy shows a typical course where the conventional alloy exceeds the limiting value according to the German DrinkwR after nine weeks and slowly falls back again towards the limiting value of the DrinkwR after a maximum approximately in the 18^(th) week. It is true that the increase of the nickel concentration in the drinking water by the red-bronze alloy B could yet not be exactly explained. However, the increase is reproducible. The limiting value given by the DrinkwR is not observed.

In comparison thereto, the copper alloy A according to the invention does not emit any mentionable nickel ions into the drinking water. Here, too, the measured values of approximately 2 μg/l are within the range of discrimination of the analysis used in the measuring devices.

In the copper emission (FIG. 3), the two compared alloys show essentially the same course. The alloy A according to the invention, however, takes lower values for the copper emission in μg/l within the timely significant test results. The maximum for both alloys is the measured value after 18 test weeks. Then, the copper emission is reduced for both alloys. The better migration values for the element copper with respect to conventional red bronze evidence the improved corrosion resistance of the alloy according to the invention and were first not to be expected as the alloy according to the invention has a higher copper proportion than conventional red bronze. It showed, however, that just this high copper proportion of 80% and more represents the essential cause for the improved migration behavior. By the way, both alloys have a sufficient distance to the W(15-value) even when they have reached their maximum. Taking into consideration the test set-up, thus an observation of the limiting values according to the DrinkwR results. In a comparison, however, it strikes that the alloy A according to the invention has a more favorable behavior with respect to the conventional alloy B with a difference amount of approx. 500 μg/l, corresponding to 20 to 25%.

Finally, FIG. 4 shows the amount of zinc emitted into the drinking water by the alloy. For zinc, no limiting value have been determined according to the DrinkwR. The course for the zinc emission in the copper alloy A according to the invention differs considerably from the corresponding course for the comparison alloy B. The migration of the embodiment A of the alloy of zinc according to the invention is at any time below 100 μg/l. The conventional alloy B exceeds this value many times over.

The diagrams shown in FIGS. 1 to 4 illustrate the advantages of the copper alloy according to the invention, in particular the influence of the silicon for the suppression of undesired metal ion migration into the drinking water. 

1. Use of a copper alloy for the manufacture of components for gas or water lines which carry media, in particular drinking water lines as well as fittings and valves of the same, wherein the copper alloy comprises, in % by weight: 2.8≦Si≦4.5; 1≦Zn≦15; 0.05≦Mn≦2; 80≦Cu≦96.95 optionally further comprising; 0.05≦Al≦0.5 0.05≦Sn≦2; 0.0005≦Zr≦0.05 0.01≦P≦0.2 and unavoidable impurities.
 2. Use according to claim 1, characterized in that the copper alloy is used for the manufacture of compression joints.
 3. Use according to claim 1, characterized in that the copper alloy is used for the manufacture of valves with a fixed compression connection.
 4. Use according to claim 1, characterized in that 5% by weight≦Zn≦15% by weight.
 5. Use according to one of claims 1 to 4, characterized in that 0.2% by weight≦Mn≦0.6% by weight.
 6. Use according to claim 5, characterized in that the unavoidable impurities are contained with not more than altogether 0.5% by weight.
 7. Use according to claim 6, characterized in that the unavoidable impurities are contained with not more than altogether 0.25% by weight.
 8. Use according to claim 6 or 7, characterized in that Ni and/or Pb are contained as unavoidable impurities with not more than altogether 0.25% by weight.
 9. Components for gas or water lines which carry media, in particular drinking water lines as well as fittings and valves of the same, at least partially consisting of a copper alloy, comprising in % by weight: 2.8≦Si≦4.5; 1≦Zn≦15; 0.05≦Mn≦2; 80≦Cu≦96.95 optionally further comprising; 0.05≦Al≦0.5 0.05≦Sn≦2; 0.0005≦Zr≦0.05 0.01≦P≦0.2 and unavoidable impurities.
 10. Component according to claim 9, characterized in that the elements Cu, Zn and Si are present in an amount of more than 98% by weight in the form of an α-solid solution.
 11. Components according to claim 9, characterized in that the components are compression joints.
 12. Components according to claim 11, characterized in that the components are valves with fixed compression connection.
 13. Component according to claims 9 or 11, characterized in that 5% by weight≦Zn≦15% by weight.
 14. Component according to claims 9 or 11, characterized in that 0.2% by weight≦Mn≦0.6% by weight.
 15. Component according to claim 9, characterized in that the unavoidable impurities are contained with altogether not more than 0.5% by weight.
 16. Component according to claim 15, characterized in that the unavoidable impurities are contained with altogether not more than 0.25% by weight.
 17. Component according to claim 15, characterized in that Ni and/or Pb are contained as unavoidable impurities with altogether not more than 0.25% by weight.
 18. Components for gas or water lines which carry media, in particular drinking water lines as well as fittings and valves of the same, at least partially consisting of a copper alloy, comprising in % by weight: 2.8≦Si≦4.5; 1≦Zn≦15; 0.05≦Mn≦2; 80≦Cu≦96.95 optionally further comprising; 0.05≦Al≦0.5 0.05≦Sn≦2; 0.0005≦Zr≦0.05 0.01≦P≦0.2 and unavoidable impurities and wherein the elements Cu, Zn and Si are present in an amount of more than 98% by weight in the form of an α-solid solution.
 19. Components according to claim 18, characterized in that the components are compression joints.
 20. Components according to claim to 18, characterized in that the components are valves with fixed compression connection.
 21. Component according to claim 18, characterized in that 5% by weight≦Zn≦15% by weight.
 22. Component according to claim 18, characterized in that 0.2% by weight≦Mn≦0.6% by weight.
 23. Component according to claim 18, characterized in that the unavoidable impurities are contained with altogether not more than 0.5% by weight.
 24. Component according to claim 23, characterized in that the unavoidable impurities are contained with altogether not more than 0.25% by weight.
 25. Component according to claim 18 or 24, characterized in that Ni and/or Pb are contained as unavoidable impurities with altogether not more than 0.25% by weight. 